A presumption of laches arises when the delay between actual or constructive notice of potential infringement and the filing of a lawsuit exceeds six years.

Opinion (Stark): St. Clair Intellectual Prop. Consultants, Inc. ("St. Clair") sued Acer, Inc. and several other computer manufacturers ("Acer") alleging infringement of several patents related to CPU power management. Acer moved for summary judgment that the doctrine of laches prevented St. Clair from pressing its claims. Laches is a defense against claims of patent infringement. The doctrine requires the party asserting the defense show by a preponderance of the evidence that: 1) the patent holder’s delay in bringing suit was unreasonable and inexcusable, and 2) that the alleged infringer suffered material prejudice as a result. If the patentee waits six or more years from the time it has actual or constructive notice of the potential infringement, before it files suit, a presumption of laches arises. St. Clair purchased a subset of the patents at issue in 2000. Prior to its acquisition of the patents, the inventor of the patents informed St. Clair that Intel may have been infringing one of the patents. By 2002, St. Clair had received claim charts for use in potential infringement actions against the manufactures. Despite this information, however, St. Clair did not file suit until May, 2009. Because the delay between the latest date at which St. Clair received notice of the potential infringement and the date it finally filed suit was more than six years, the presumption of laches was established. To rebut the presumption, the patentee must show that the delay was reasonable. St. Clair attempted to argue that the cost and difficulty of investigating the potential claims excused the delay. Because it had completed claim charts in 2002, however, the court refused to accept this argument and GRANTED the motion for summary judgement in favor the manufactures.